Non-antigenic branched polymer conjugates

Abstract: Branched, substantially non-antigenic polymers are disclosed. Conjugates prepared with the polymers and biologically active molecules such as proteins and peptides demonstrate extended circulating life in vivo . Substantially fewer sites on the biologically active material are used as attachment sites. Methods of forming the polymer, conjugating the polymers with biologically active moieties and methods of using the conjugates are also disclosed.

Description: Field of the Invention The present invention relates to branched polymers which are useful in extending the in vivo circulating life of biologically active materials. The invention also relates to conjugates made with the polymers. Some of the initial concepts of coupling peptides or polypeptides to poly(ethylene glycol) PEG and similar water-soluble poly(alkylene oxides) are disclosed in U.S. Patent No. 4,179,337, the disclosure of which is incorporated herein by reference. Polypeptides modified with these polymers exhibit reduced immunogenicity/antigenicity and circulate in the bloodstream longer than unmodified versions. To conjugate poly(alkylene oxides), one of the hydroxyl end-groups is converted into a reactive functional group. This process is frequently referred to as "activation" and the product is called an "activated poly(alkylene oxide)". Other substantially non-antigenic polymers are similarly "activated" or functionalized. The activated polymers are reacted with a therapeutic agent having nucleophilic functional groups that serve as attachment sites. One nucleophilic functional group commonly used as an attachment site is the ∈-amino groups of lysines. Free carboxylic acid groups, suitably activated carbonyl groups, oxidized carbohydrate moieties and mercapto groups have also been used as attachment sites. Insulin and hemoglobin were among the first therapeutic agents conjugated. These relatively large polypeptides contain several free ∈-amino attachment sites. A sufficient number of polymers could be attached to reduce immunogenicity and increase the circulating life without significant loss of biologic activity. Excessive polymer conjugation and/or conjugation involving a therapeutic moiety's active site where groups associated with bioactivity are found, however, often result in loss of activity and thus therapeutic usefulness. This is often the case with-lower molecular weight peptides which have few attachment sites not associated with bioactivity. Many non-peptide therapeutics also lack a sufficient number of attachment sites to obtain the benefit of polymer modification. One suggestion for overcoming the problems discussed above is to use longer, higher molecular weight polymers. These materials, however, are difficult to prepare and expensive to use. Further, they provide little improvement over more readily available polymers. Another alternative suggested is to attach two strands of polymer via a triazine ring to amino groups of a protein. See, for example, Enzyme , 26 , 49-53 (1981) and Proc. Soc. Exper. Biol. Med. , 188 , 364-9 (1988). Research in this area has continued. Triazine is a toxic substance which is difficult to reduce to acceptable levels after conjugation. In addition, triazine is a planar group and can only be double-polymer substituted. The planar structure rigidly locks the two polymer chains in place. This limits the benefits of polymer conjugation to about the same as that obtained by increasing polymer chain length. Thus, non-triazine-based activated polymers would offer substantial benefits to the art. The present invention addresses this need. DESCRIPTION OF THE INVENTION This invention provides a polymer conjugate, obtainable by reacting a branched substantially non-antigenic polymer having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile, with a biologically active nucleophile. More particularly, the invention provides a polymer conjugate as defined above, having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; (nucleophile) is a biologically active nucleophile; and z is an integer ≥ 1. Preferably, the biologically active nucleophile is a protein, peptide or polypeptide. In one embodiment, the biologically active nucleophile is erythropoietin. In another embodiment, the biologically active nucleophile is Tumor Necrosis Factor. In again another embodiment, the biologically active nucleophile is an α-, β- or γ-interferon. This invention further provides a method of forming a polymer conjugate, comprising reacting a branched substantially non-antigenic polymer having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile, with a biologically active nucleophile. In one embodiment of said method, a conjugate is formed having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; (nucleophile) is a biologically active nucleophile; and z is an integer ≥ 1. Further, this invention provides a branched substantially non-antigenic polymer having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile. More particularly, the invention provides a branched substantially non-antigenic polymer as defined above, having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; and A is a functional group capable of bonding with a biologically active nucleophile or a moiety capable of being functionalized to react with a biologically active nucleophile. One of the chief advantages of the present invention is that the branching of the polymers imparts an umbrella-like three-dimensional protective covering to the materials they are conjugated with. This contrasts with the string-like structure of conventional polymer conjugates. Moreover, the branching of the polymer chains from a common root allows dynamic, non-planar action in vivo . Thus, the branched polymers offer substantial benefits over straight-chained polymers of equivalent molecular weight. A second advantage of the branched polymers is that they provide the benefits associated with attaching several strands of polymers to a bioeffecting material but require substantially fewer conjugation sites. The advantages of the branched polymers are particularly dramatic for therapeutic agents having few available attachment sites. All the desired properties of polymer conjugation are realized and loss of bioactivity is minimized. It is preferred that each mPEG chain has a molecular weight of between about 200 and about 12,000 daltons and preferably between about 1,000 and about 10,000 daltons. Molecular weights of about 5,000 daltons are most preferred. The moiety (A) represents groups that "activate" the branched polymers of the present invention for conjugation with biologically active materials. (A) can be a moiety selected from: I. Functional groups capable of reacting with an amino group such as: a) carbonates such as the p-nitrophenyl, or succinimidyl; b) carbonyl imidazole; c) azlactones; d) cyclic imide thiones; or e) isocyanates or isothiocyanates. II. Functional groups capable of reacting with carboxylic acid groups and reactive carbonyl groups such as: a) primary amines; or b) hydrazine and hydrazide functional groups such as the acyl hydrazides, carbazates, semicarbamates, thiocarbazates, etc. III. Functional groups capable of reacting with mercapto or sulfhydryl groups such as phenyl glyoxals; see, for example, U.S. Patent No. 5,093,531, the disclosure of which is hereby incorporated by reference. IV. Other nucleophiles capable of reacting with an electrophilic center. A non-limiting list includes, for example, hydroxyl, amino, carboxyl, thiol groups, active methylene and the like. The branched polymers (U-PEG's) are formed using conventional reaction techniques. After synthesis, the activated branched polymers can be purified by conventional methods and reacted with biologically active materials containing nucleophiles capable of bonding with the polymer while maintaining at least some of the activity associated with the material in unmodified form. The nucleophiles conjugated with the branched polymers are described as "biologically active". The term, however, is not limited to physiological or pharmacological activities. For example, some nucleophile conjugates such as those containing enzymes, are able to catalyze reactions in organic solvents. Likewise, some inventive polymer conjugates containing proteins such as concanavalin A, immunoglobulin and the like are also useful as laboratory diagnostics. A key feature of all of the conjugates is that at least some portion of the activity associated with the unmodified bio-active material is maintained. The conjugates are biologically active and have numerous therapeutic applications. Mammals in need of treatment which includes a biologically active material can be treated by administering an effective amount of a polymer conjugate containing the desired bioactive material. For example, mammals in need of enzyme replacement therapy or blood factors can be given branched polymer conjugates containing the desired material. Biologically active nucleophiles of interest of the present invention include, but are not limited to, proteins, peptides, polypeptides, enzymes, organic molecules of natural and synthetic origin such as medicinal chemicals and the like. Enzymes of interest include carbohydrate-specific enzymes, proteolytic enzymes, oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Without being limited to particular enzymes, examples of enzymes of interest include asparaginase, arginase, arginine deaminase, adenosine deaminase, superoxide dismutase, endotoxinases, catalases, chymotrypsin, lipases, uricases, adenosine diphosphatase, tyrosinases and bilirubin oxidase. Carbohydrate-specific enzymes of interest include glucose oxidases, glucodases, galactosidases, glucocerebrosidases, glucouronidases, etc. Proteins, polypeptides and peptides of interest include, but are not limited to, hemoglobin, serum proteins such as blood factors including Factors VII, VIII, and IX; immunoglobulins, cytokines such as interleukins, α-, β- and γ-interferons, colony stimulating factors including granulocyte colony stimulating factors, platelet derived growth factors and phospholipase-activating protein (PLAP). Other proteins of general biological or therapeutic interest include insulin, plant proteins such as lectins and ricins, tumor necrosis factors and related alleles, growth factors such as tissue growth factors, such as TGFα's or TGFβ's and epidermal growth factors, hormones, somatomedins, erythropoietin, pigmentary hormones, hypothalamic releasing factors, antidiuretic hormones, prolactin, chorionic gonadotropin, follicle-stimulating hormone, thyroid-stimulating hormone, tissue plasminogen activator, and the like. Immunoglobulins of interest include IgG, IgE, IgM, IgA, IgD and fragments thereof. Some proteins such as the interleukins, interferons and colony stimulating factors also exist in non-glycosylated form, usually as a result of using recombinant techniques. The non-glycosylated versions are also among the biologically active nucleophiles of the present invention. The biologically active nucleophiles of the present invention also include any portion of a polypeptide demonstrating in vivo bioactivity. This includes amino acid sequences, antisense moieties and the like, antibody fragments, single chain binding antigens, see, for example U.S. Patent No. 4,946,778, disclosure of which is incorporated herein by reference, binding molecules including fusions of antibodies or fragments, polyclonal antibodies, monoclonal antibodies, catalytic antibodies, nucleotides and oligonucleotides. The proteins or portions thereof can be prepared or isolated by using techniques known to those of ordinary skill in the art such as tissue culture, extraction from animal sources, or by recombinant DNA methodologies. Transgenic sources of the proteins, polypeptides, amino acid sequences and the like are also contemplated. Such materials are obtained form transgenic animals, i.e., mice, pigs, cows, etc., wherein the proteins expressed in milk, blood or tissues. Transgenic insects and baculovirus expression systems are also contemplated as sources. Moreover, mutant versions of proteins, such as mutant TNF's and/or mutant interferons are also within the scope of the invention. Other proteins of interest are allergen proteins such as ragweed, Antigen E, honeybee venom, mite allergen, and the like. Useful biologically active nucleophiles are not limited to proteins and peptides. Essentially any biologically-active compound is included within the scope of the present invention. The present invention is particularly well-suited for compounds which have few or even a single nucleophilic attachment site for polymer conjugation such as medicinal chemicals whether isolated from nature or synthesized. Chemotherapeutic molecules such as pharmaceutical chemicals i.e. anti-tumor agents, cardiovascular agents, anti-neoplastics, anti-infectives, anti-anxiety agents, gastrointestinal agents, central nervous system-activating agents, analgesics, fertility or contraceptive agents, anti-inflammatory agents, steroidal agents, anti-urecemic agents, cardiovascular agents, vasodilating agents, vasoconstricting agents and the like. The foregoing is illustrative of the biologically active nucleophiles which are suitable for conjugation with the polymers of the invention. It is to be understood that those biologically active materials not specifically mentioned but having suitable nucleophilic groups are also intended and are within the scope of the present invention. One or more of the activated branched polymers can be attached to a biologically active nucleophile by standard chemical reactions. The degree of conjugation can be modified by varying the reaction stoichiometry using well-known techniques. More than one polymer conjugated to the nucleophile can be obtained by reacting a stoichiometric excess of the activated polymer with the nucleophile. The biologically active nucleophiles can be reacted with the activated branched polymers in an aqueous reaction medium which can be buffered, depending upon the pH requirements of the nucleophile. The optimum pH for the reaction is generally between about 6.5 and about 8.0 and preferably about 7.4 for proteinaceous/polypeptide materials. Organic/chemotherapeutic moieties can be reacted in non-aqueous systems. The optimum reaction conditions for the nucleophile's stability, reaction efficiency, etc. is within level of ordinary skill in the art. The preferred temperature range is between 4°C and 37°C. The temperature of the reaction medium cannot exceed the temperature at which the nucleophile may denature or decompose. It is preferred that the nucleophile be reacted with an excess of the activated branched polymer. Following the reaction, the conjugate is recovered and purified such as by diafiltration, column chromatography, combinations thereof, or the like. It can be readily appreciated that the activated branched non-antigenic polymers of the present invention are a new and useful tool in the conjugation of biologically active materials, especially when they lack a sufficient number of suitable polymer attachment sites. EXAMPLES The following non-limiting examples illustrate certain aspects of the invention. All parts and percentages are by weight unless otherwise noted and all temperatures are in degrees Celsius. MATERIALS Methoxypoly(ethylene glycol) (m-PEG) was obtained from Union Carbide. The solvents were obtained from Aldrich Chemical of Milwaukee, Wisconsin. The methoxy-poly(ethylene glycol)-N-succinimidyl carbonate (SC-PEG) was prepared as described in U.S. Patent No. 5,122,614, using m-PEG having a molecular weight of about 5,000. Each of the products prepared were confirmed structurally by carbon - 13 NMR. EXAMPLE - (a) U-LYS-PEG The branched polymer depicted above was prepared by reacting m-PNP - PEG with lysine ethyl ester. In particular, a mixture of 5.0 g (1.0 mmol) of the polymer, 150 mg (0.6 mmol) of lysine dihydrochloride and 140 mg (1.8 mmol) of pyridine was refluxed for 18 hours. The solvent was removed by distillation in vacuo . The residue was recrystallized from 2-propanol to yield 4.5 g (88% yield) of product. (b) Synthesis of m-PNP-PEG A solution of 50g (0.01 moles) of m-PEG-OH (MW=5000) in 500ml of toluene was azeotroped for 2 hrs, while removing 100ml of toluene/water. The reaction mixture was cooled to 30°C, followed by addition of 2.6 g (0.013 moles) of p-nitrophenyl chloroformate and 1.0 ml (0.013 moles) of pyridine. The resulting mixture was stirred for two hours at 45°C, followed by stirring overnight at room temperature. The reaction mixture was then filtered through CELITE™, followed by removal of the solvent by distillation in vacuo . The residue was recrystallized from 2-propanol to yield 48.2g (93% yield) of the product.

Claims: A polymer conjugate, obtainable by reacting a branched substantially non-antigenic polymer having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile, with a biologically active nucleophile. A polymer conjugate according to Claim 1 having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; (nucleophile) is a biologically active nucleophile; and z is an integer ≥ 1. A polymer conjugate according to Claim 1 or 2, wherein the biologically active nucleophile is a protein, peptide or polypeptide. A polymer conjugate according to Claim 3, wherein the biologically active nucleophile is erythropoietin. A polymer conjugate according to Claim 3, wherein the biologically active nucleophile is Tumor Necrosis Factor. A polymer conjugate according to Claim 3, wherein the biologically active nucleophile is an α-, β- or γ-interferon. A method of forming a polymer conjugate, comprising reacting a branched substantially non-antigenic polymer having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile, with a biologically active nucleophile. A method according to Claim 7 wherein a conjugate is formed having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; (nucleophile) is a biologically active nucleophile; and z is an integer ≥ 1. A method according to Claim 7 or 8, wherein the biologically active nucleophile is a protein, peptide or polypeptide. A method according to Claim 9, wherein the biologically active nucleophile is erythropoietin. A method according to Claim 9, wherein the biologically active nucleophile is Tumor Necrosis Factor. A method according to Claim 9, wherein the biologically active nucleophile is an α-, β- or γ-interferon. A branched substantially non-antigenic polymer having the formul wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol, or an activated form thereof capable of reacting with a biologically active nucleophile. A branched substantially non-antigenic polymer according to Claim 13 having the formula: wherein mPEG is a water soluble, substantially non-antigenic methoxy polyethylene glycol; and A is a functional group capable of bonding with a biologically active nucleophile or a moiety capable of being functionalized to react with a biologically active nucleophile.

Inventors: GREENWALD RICHARD B, MARTINEZ ANTHONY, GREENWALD, RICHARD B., MARTINEZ, ANTHONY
Applicants: ENZON INC, ENZON, INC.
Application year: 1994
Main classification: C07K17
IPC codes: C08G65, C07K17, A61K47